Ultrasonic time reversal based imaging for extended target

In this paper, the time reversal based imaging methods have been used in the area of ultrasonic Non-destructive evaluation (NDE) for extended target, the size of which is on the order of the ultrasonic wavelength or larger. Both time reversal with multiple signal classification (TR-MUSIC) and phase-coherent multiple signal classification (PC-MUSIC), the two typical time reversal based imaging methods, have been introduced to obtain the ultrasonic image by post-processing the pulse-echo signals belonging to the ultrasonic array data. Experimental system has been designed and built to capture the real ultrasonic array data via full matrix capture (FMC) process from the test sample. The experiment was implemented on a block of Al with Electrical Discharge Machining (EDM) line, which can be considered as the extended target. The experimental results show that PC-MUSIC over the given frequency range can provide the shape and size of the extended target, however, TR-MUSIC fails. In addition, the various dimensions of signal subspace are chosen, and its effect on the imaging result has been studied.